DETERMINATION AND ROTAMER SEPARATION OF ENALAPRIL MALEATE BY CAPILLARY ELECTROPHORESIS

Capillary electrophoresis (CE) was applied to the study of enalapril maleate, an inhibitor of angiotensin-converting enzyme. By the use of capillary zone electrophoresis, a method using sodium borate or sodium phosphate buffers (pH 8.25-9.7) as an electrolyte and using an external standard was developed for the determination of enalapril maleate at room temperature. At a method concentration of 0.2 mg/ml, the injection precision (R.S.D. = 0.62%, n = 10) and linearity of detector responses (range 50-150% of the method concentration, R2 = 0.999) were satisfactory. The method precision was also satisfactory as demonstrated by the content uniformity assays of ten tablets of Vasotec (20 mg potency). The method is stability indicating and specific as enalapril can be well separated from its two degradates, enalaprilat (a hydrolysis product) and its diketopiperazine (a cyclization product). By the use of micellar elektrokinetic capillary chromatography, in which 40-100 mM sodium dodecyl sulfate were added to the electrolyte buffers to form micelles in capillary, the cis and trans rotamers of enalapril was separated at or below 20-degrees-C. As the temperature increased, the two peaks spread and coalesced to one peak above 40-degrees-C. The study demonstrates that CE can be effectively applied to both the determination and conformer separation of drugs in pharmaceutical research and development.